The present invention is directed to a size reduction device and especially a granulator such that scrap plastic material may be granulated for reprocessing. Devices of this general nature are in common application throughout the plastics industry. Desirable features of such devices include operation at relatively low energy consumption and noise levels, minimum production of fines, smooth intake of the scrap material to the device without excessive fly back or bounce back thereof, satisfactory knife life and the ability to resharpen the knives without undesirably affecting the operation of the device, and even loading of operational bearings so as to insure satisfactory wear or avoidance of oversized bearings.
While known devices accomplish several of these desirable objectives, there remains a need for a single machine which fulfills all of such objectives in an efficient and trouble-free manner. Thus, for example, it is known to angle either a rotor or bed knife for coation with an opposed straight knife such that the knives progressively move past each other, thus avoiding cutting material across the full lengths thereof at one time. Such angled knife construction serves to reduce power consumption and noise levels to some extent since material is being progressively cut. It is also known to angle both the rotor blade and the bed knife such that a scissors type cutting action is set up, however, constructions of this type while producing favorable cutting action when the knives are new and thus present and even gap along the opposed cutting edges as they progressively move past each other, present problems when the knives are dull. Under dulled and thus unfavorable cutting conditions, the material initially contacted by the cutting nip tends to laterally push the material to one side of the granulator, thus requiring more cutting action by the blade portion disposed at that side. Uneven wear of the blades thus occurs. Such construction, by reason of its tending to push material towards one side of the chamber, also builds up frictional heat and places a greater force on the rotor bearing on that side of the chamber resulting in an unbalanced load and requirement to either use oversized or special bearings. This condition is also undesirable in that it tends to create fines by the continued rubbing of the laterally forced material up against the far chamber side.
The above-discussed blade construction also do not adequately clamp or progressively engage articles disposed therebetween and enable the articles to some extent undesirably squirm or move about prior to initiating a cutting or breaking action. Such undesirable squirm to some extent has been eliminated by the use of a chevron figured rotor blade construction moving past a straight bed knife. It is also known to utilize the dual chevron configuration in which the central peak of both the rotor and bed knife are directed towards each other so as to initiate a central cut on opposite sides of the article being granulated, although such construction also tends to force material to both sides of the granulator chamber inasmuch as a dual scissor cut action is in reality set up and thus results in undesirable fines and frictional heat.
It is accordingly a primary object of the present invention to provide a size reduction device of the present type which avoids the above-discussed prior art drawbacks and which simultaneously accomplishes all of the aforementioned desirable objectives.
This and other objects of the present invention are accomplished by a device for the size reduction of material comprising a frame, a chamber, a rotor mounted for rotation about an axis within said chamber, cutting means affixed to said rotor, bed knife means mounted on said frame for projection into said chamber thereof for cooperative cutting relationship with said cutting means as said rotor is driven, said cutting means including a rotor blade extending laterally across the face of said rotor with the forward cutting edge thereof defining the circumferential cutting plane of said rotor, said rotor blade of an overall generally chevron configuration having side portions thereof laterally angularly slanted towards each other to define a central peak thereof, said peak being further arcuately displaced from a radial plane passing through the laterally spaced sides of said blade in a rotational direction opposite to that of said rotor said bed knife means including a similarly chevron shaped bed knife disposed with the peak thereof directed opposite to that of said rotor blade and with the cutting edge thereof radially outwardly offset from said rotor blade and further disposed with the peak thereof arcuately displaced from the sides thereof in the opposite direction of the displacement of said rotor blade such that the cutting edges of said blades may progressively pass across each other in evenly spaced relationship and form a progressively flatter generally trapezoidal opening therebetween upon such relative motion whereby articles to be cut thereby are contacted by said blades at laterally spaced locations on opposite surfaces thereof so as to clamp said articles within said opening.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.